1. Field of the Invention
This invention relates to a heating apparatus such as microwave ovens wherein the type of food contained in a heating chamber is determined on the basis of a change rate of volume of gas emanated from the food in the heating chamber.
2. Description of the Prior Art
Heating apparatus such as microwave ovens have recently been provided with a gas sensor for sensing gas emanated from food to be cooked so that the type of the food is determined on the basis of an output of the gas sensor and the heating operation is controlled in accordance with the result of determination. More specifically, the employed gas sensor is particularly sensitive to a volatile high polymer gas. A change rate of an output of the gas sensor or a change rate of gas volume is calculated by a control circuit. The obtained change rate of the gas volume is compared with a previously set reference value. On the basis of the result of comparison, it is determined whether the type of the food to be heated is one containing a large volume of gas or not.
However, an initial temperature in the heating chamber takes different values, for example, when the heating operation is performed a relatively long period of time after the last operation and when the heating operation is repeated at one time. Furthermore, a generation rate of the gaseous alcohol varies depending upon the initial temperature in the heating chamber. In view of these facts, the type of the food determined in the manner as described above sometimes differs from an actual type of the food. The reason for this is that employment of a fixed reference value results in errors in the determination of the type of the food.